Method of lining and insulating the interior surfaces of continuously operated furnaces



1 May 9,'1944. L. LARsoN 2,343,395

METHOD OF LINING AND' INSULATING'-THE INTERIOR SURFACE OF COVNTINUOUSLY OPERTED FURNACES Filed Dec. e, 1941 A40/s rues Mawr/ED SmeMe-.e Wsw/werfe Sf/.saePo/Nrs 624,145'

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24 ATTORNEY Patented May 9, 1944 UNITED STATES PATENT OFFICE METHOD or LINING-AND` INSULAT'ING THE marcaron sUaFAcEs or ooN'rINUoUsLY oramirnn FUnNAoEs Leonard Larson, McGill, Nev., assignor to Kennecott Corporation, New York, N. Y., a corporation of New York application December s, 1941, serial No. 422,039 s oiainis. (ci. '26e-43) This invention relates to lining and insulating procedures whereby the heated interior surfaces of a furnace or the like may be provided with a protective cellular refractory coating without interference with the furnace operation.

It is well known that the refractory linings of, high temperature furnaces are subject to deterioration by the fluxing and. eroding action of dust-laden furnace gases, and procedures have heretofore been advanced whereby certain types of furnaces can bemaintained in operative con dition over long periods of time by the application of refractory coatings to the heated interior surfaces Aduring the course of the furnace operation, and this invention is considered to be an improvement over the heretofore suggested processes of this character.

One of the particular objects of this invention is to provide a method for lining and thus protecting the interior surfaces of a continuously operated furnace or the like, in which a highly plastic argillaceous material, particularly one having pronounced thixotropic propertes is applied in the form of a thick layer to the heated furnace surface for which protection is desired. 'I'his technique is in contradistinction to the hitherto-accepted procedure, and as a `result thereof certain advantages are gained, as hereinafter more particularly set forth.

A further object of the invention is to provide a process of the character described, in which a highly plastic aqueous argillaceous mixture is applied in thick layers to the heated surface to secure the evolution of moisture in the form of steam Within the applied plastic material (caused by the rapid heating effect upon the water contained in the plastic mixture), to cause a physical swelling of the plastic material, in situ, which re- 'sults in the creation of a highly cellular struc-l ture in the applied layer before the plasticity tion value owing to the low bulk density resulting from the porous structure.

In the accompanying drawing Fig. 1 shows, in graphical form, the relation between viscosity and moisture content in five different plastic compositions, in illustration of certain aspects of this invention, and Fig. 2 illustrates a form of apparatus by means of which the plastic argillaceous compositions may be forced into impingement upon the furnace surfaces to be insulated.

The invention is particularly directed to the, coating of interior surfaces of reverberatory furnaces, and the like, such as are employed for example in the copper smelting industry for the smelting of copper-bearing calcines, concentrates, ores and fluxes in the production of copper matte and slag. Itsapplication to other types of furnaces, however, Will'be apparent to those skilled in the art. In the operation of a rever-` beratory furnace it is desirable to maintain an operating campagin of the longest practicable period, wherefore the composition applied is preferablyvone having a marked tendency to adhere to the interior surfaces qof the furnace, and to resist the iiuxing and eroding action of the dustbearing furnace gases. The lining customarily employed in the rreverberatory' furnace is of a siliceous nature, such as silica brick, andthe coating material may therefore, in the usual case, be of a predominately siliceous nature.

According to practice of the present invention, I apply to the heated surface to be treated a rather heavy, preferably highly plastic, aqueous argillaceous mixture, in such manner that the maximum thickness of coating is secured in a single application, to which successive coatings thereof has been reduced (by moisture evaporation) to a point such that fracture (spalling) would result.

A further object of the invention is to provide a met odof applying a plastic mixture to a heated furnace surface in the form:ofsuccessivc r "slugs" of the composition,- instead of in the form of a spray or thin slurryv as has heretofore been recommended, whereby the composition is applied as a rather thick coating within which the aforementioned swelling and cellular structure formation may take place, in the production of a highly refractory, strongly adhering porous ceramic layer upon the surface to-be treated, which layer has an appreciable thermal insulamay be applied in building up a layer .of thedesired ultimate thickness.

'I'he plastic mixture is'applied in the form of successive slugs rather than as a continuous stream, such slugs being applied successively to adjacent areas to cover a given area of the furnace surface, and repeated applications being made to secure a layer of the required thickness. arepreferably not madey to a specific area untilthe material rst applied has had an opportunity to swell and expand into the above-described porous structure, in order to secure with a given volume of material the maximum percentage application to the surface under treatment.

It has been determined that the plastic argillaceous mixture must be such as to have several distinct but related properties in order that the The repeated applications maximum benefits of the process are attained, among which may be listed:

(a) Refractoriness.-This property is primarily a function of the chemical constitutionof the various ingredients of the mixture, taken' with the particle size of the respective ingredients, and may be controlled according to well-known principles of the ceramic art. The refractoriness of a particular plastic mixture to be used in the process will be established in relation to the heat condition to which the protecting layer will be subjected; in general, at a 4point above the normal operating temperathe melting point of the layer will be established ture of the furnace.

(b) High plasticity (consistency) .-This property is primarilya function of the character and the amount of the colloidalmaterial'present in the aqueous mixture, in relation to the proportion of moisture present. For the practice of the present process, it has been found that the `consistency of the plastic mixture should be such that the shear-point, as determined with a socalled modified Stormer viscometer, is Within a range from about 100 grams to about 3000 grams, preferably within a range of about 800 grams to about.2500 grams, and -more preferably Within a range of about 1300 to about 2200 grams.

(c) High moisture content-This is also a function of the character and amount of colloidal matter present in the composition, and it has been found that a moisture content in excess of about 30% is essential in order that the desired porous condition is produced in the final bricked layer of protective coating. The. moisture content may be established at a value of 50% or more, depending upon the amount 'of and character of the colloidal material employed, without departing from the consistency range set forth above.k

(d) Thotropy.-This property has been defined as the tendency for a plastic material to change reversibly from a gel t'o a sol under mechanical action, and it` has been found that the maximum benefits of the process of the present invention are attained where the plastic aqueous argillaceous mixture is one exhibiting marked thixotropic properties. This property contributes particularly to the behavior of the material when' the slugs thereof are formed and applied to the surface to be treated, as well as to the behavior of the plastic mixturetimmediately following its application.

de) High dry strength-This property is primarily a function of the proportion o f colloidal argillaceous particles inthe mixture, and may be determined according to the accepted procedure employed by ceramists. I have determined that the dry strength of the mix` employed. should preferably be such that the modulus of rupture is in the neighborhood of 100 pounds per square inch or more, as determined according to the conventional formula:

- positions should bekep't as low as possible, in

order to minimize spalling in the moisture-evolution stage and the subsequent firing stage durful in this connection. The so-called high-plasplastic argillaceous mixture, it may be said that' such mixture should be formed of materials having the desired refractory qualities, a high drystrength upon evaporation of the contained moisture, is preferably markedly thixotropic, and should have a high plasticity. Eor the most part these properties contribute to a marked tendency for the material to, (a) while in the plastic state, to adhere to the furnace surface when applied; (b) to swell .into the desired porous state as the result of the evolution of steam' within the still plastic mass as it is reduced to dryness; (c) to persist in place during the moisture evolution stage and the subsequent firin stage during which the applied layer is brought 'up to the furnace temperature and converted into what may be termed a bricked layer, without spalling;

and (d) to persist in place after conversion into the desired insulating bricked layer, without undue spalling, erosion, or fluxing.

The selection of raw materials for use in compounding the plastic argillaceous mixture, and the establishment of the desired water content therein, will be controlled by two separate and relatively unrelated criteria: refractoriness, and physical behavior during and shortly after the application. The operating conditions to which tion thereof. As above pointed out, a minimum water proportion of about 30%, by weight, has been'found tovbe essential, in order to cause the production of an adequately porous layer of appreciable thickness which can be built up into an insulative and protective coating. This lower limit on the moisture content, taken with the plasticity or consistency limits of this invention, makes it essential to employl a highly plastic ma# terial as a constituent of the mixture, and I have determined that a material of the character of a swelling type of bentonite is particularly useticityv `fire-clays are also useful, or mixtures thereof with a material such as bentonite, provided the desired consistency and minimum water content limitations are met in the compounding.

IWhen the composition is to be used in lining a furnace constructed of silica brick, for example, I preferably employ a material such as silica flour as the main solid constituent of the plastic argillaceous mixture. In order to secure the desired consistency, and to produce the preferable thixotropic property, I mix with such silica flour a. highly colloidal clay material, together with the requisite amount of water. The greater the amount of highly colloidal clay material which is incorporated in the mixture, the greater the amount of water which can be intermixed without departing from the useful range of consistencies.

The upper limit on the quantity of highly colinthe still plastic mass@ bricked layer to be formed on the furnace surface, it being appreciated, for example, that the greater the proportion of bentonite in a bentonitersilica our mixture, the lower' will be the melting point of the fired and bricked layer. I have prepared useful bentonite:silica flour mixtures containing as 'little as 3% bentonite on a dry basis, which mixture may be rendered plastic within the allowable limits of this invention by mixing with water so that the nal plastic mixture contains between about 29% water (thickest practicable consistency) and about 36% water (thinnest practicable consistency). If a greater proportion of bentonite is employed, a

' greater proportion of water would also be required in order to establish the consistency withln the range of thepresent invention. Forexample, using a bentonite:silica flour mixture containing 7.7% bentonite on a dry basisthe-result ant aqueous plastic mixtures may contain between about 42% and about 50% water, the lower water content providing the higher consistency. Higher proportions of bentonite require still higher proportions of water'to provide the consistency within the range of the present invention.

. The mixtures may be made up in part of a colloidal clay in addition to bentonite, if desired, and the water content correspondingly adjusted to establish the consistency of the final mix within the desired range.

VThe plastic argillaceous preferably thixotropic mix of the desiredl consistency is applied to the furnace interior in the form ofsuccessive slugs" rather than as a continuous spray of thin slurry as has been heretofore proposed. The material may be applied to the furnace surface through an elongated delivery pipe which is inserted through the furnace side wall or any suitable openingr and directed tow-ard the portion of the furnace surface which is to be coated. Owing to the fact that furnaces usually are operated at high temperatures, I preferably employ a waterjacketed delivery pipe for this purpose, in order to avoid the production of any caked lining in the delivery pipe which would interfere with and Astop the passage of the plastic material therethrough. This is particularly necessary where the rather heavy muds of this disclosure are to be applied in the form of slugs in view of the fact that the cooling effect 'obtained by the passage of the mud through the discharge pipe is quite inadequate, as compared to that resulting from the passage of a fairly large quantity of relatively thin consistency mixture through the, discharge pipe in a spraying technic.

In applying the plastic material in the form of slugs, the operator preferablymoves the discharge greater the plasticity in the originallyepplied mixture, for a given water content, the more pronounced the swelling effect during this water evaporation stage.

Depending upon the consistency (shear point) of the plastic argillaceous mixture which is applied to the surface, the operator is able to apply a layer from A inch (with the thinner mixtures) toone inch (with the thicker mixtures) in thickness. 'I'his thickness is that of the material immediately upon application, before the abovedescribed development of the porous structure has begun. The swelling and expansion resulting from the formation of water vapor in the still plastic mass takes place almost immediately, and depending upon the plasticity of the mix and the proportion of Waterl employed, the mixture will swell from three to four times before the p1asticity-has been reduced to a point such that the remaining water will be driven out of the mass without forming any additional porous structure. During this moisture-evolution stage,

therefore, the layer will develop a thickness of' from one to four inches prior to the actual firing stage yduring which the layer is brought up to furnace temperature and converted to the bricked condition.A It will be appreciated that a high dry strength composition is desirable so that there will be a minimum this drying stage, and I have found that a minimum of approximately 3% bentonite in the composition will impart a sufficient dryvstrength to substantially prevent spalling during this mois` ture-evolution stage. As soon as the layer has been converted to the "bricked condition, a successive application may be made to the same area, and in this manner I may build up layers which are a foot or more in thickness.

Within an average period of 15 minutes after application, depending on the temperature of the furnace, the mixturewill ordinarily have been ceramically bonded into the bricked form, in which form it constitutes a protectingand insu- -latlng layer for. the furnace`surface. As determined from samples of this bricked layer cut from the treated surface, it has been observed that a relatively high percentage of voids is obtained by this evolution of water vapor, and that the weight per cubic foot of this bricked mateend of the delivery pipe so as to cause succes- 1 vsive. slugs to impinge upon new areas of the furnace surfaceand form a coatingof the'desired thickness. When a slug of mixture is applied to the surface, the initial adhesion isbelieved to depend upon the plastic and thixotropic characteristics of the mixture, inasmuch as it has been observed that themore marked these properties are exhibited by the mixture, Vthe greater; the vpercentage application to the y heated furnace surface. Once the slug of mixture adheres to the heated furnace surface, the rapid heat exchange lboth fromvthe hot surface to which it is adhering vand the heated gases in the' furnace, causes the Abodynofnlxture to swell and expand due to the fo the mass, 'its plasticity is greatly reduced,` and the of water vapor f r is driven from` rial will be within the range ofY from about 23 pounds to about 35\"pounds per cubic foot. The thermal insulation value of such a material is apparent.

In contradistinctiom coatings applied with silica flour-fire clay mixtures but containing no bentonite or thixotropic properties may only be applied in layers which have densities of over 50 pounds per cubic foot, and which spall olf readily.

The consistency of the mixtures employed laccording to the present invention is such that these mixtures may properly be referred to as plastic mixtures. Some of the mixtures have been found to more closely approach a truly plastic substance than have others, but they all plied stress. In order to illustrate the plastic characteristics of the useful range of compositions which may bel employed inthe practice ofthe present invention, referenceis made to the accompanying drawing, Fig. 1 of which 'shows the relationbetween composition and the modified of spalling duringV Stormer viscometer .shear point at different moisture contents, in ve fundamental mixes.

The dry-basis composition of these mixes was as follows:

The calculated chemical analysis of these mixes is as follows:

Mix and curve designation a b c d e Pcr- Per- Per-4 I cr- Per- Cen! Cent il! mi tml au su 97.2 96.2 8a3 0.4 0.a o.1 o.1 0.2 0.2 o.1 o o o o 0.o 0.o o.1 0.o 0.o 0.1 3.2 3.o 1.5 2.o 5.7 0.o o.1 0.o 0.o 0.o

Various amounts of water were incorporated with these ve mixes, and lshear point tests were run on the resulting compositions. The instrument employed for the shear point determination was the so-called modified Stormer viscometer, as illustrated at page 1273 of Chemical Engineers Handbook? (Perry), first edition. Referring to Fig. l, it will be seen that for Mix a slightly less than 32% moisture gave a mixture of zero shear point, and that the shear points of the various compositions of less water content ro'se quite rapidly as the moisture proportion was decreased. As the proportion of highly colloidal clay material was increased as in Mix b, for example, a greater moisture proportion was required for equivalent shear values. Mix c, containing a smaller proportion of actual clay material (but obviously a 'higher proportion of colloidal clay particles) required an even greater proportion of water, and Mix e carried about 65.5% ;water at the stiifest test consistency shown in the curve (2250 grams shear point). At this same consistency,.Mix a (curve a) shows a moisture content of but about 23%.

In Fig. l it will be noted that broken vertical lines extend through the curves at the 100 gram, 1300 gram, and 2200 gram shear points. These lines are respectively designated L, M, and H. 'I'he line L represents the lowermost limit of consistency within the contemplation of this invention, inasmuch as it has been found that mixtures of a thinner consistency than the 100 gram shear point compositions willexhibit less Vthan 25% application when used on the furnace surfaces, which is too low to be economically useful.

ment now available, inasmuch as at about this value the problem of applying the material in higher, the percentage application is quite satisl factory, although shear points in the neighbor-j hood of 1300 grams or higher are the more use! ful. As the consistency approaches about 2500` grams shear point, the mechanical difficulty ofI application of the composition to the furnace surface becomes quite a factor.4 At these high- A consistencies, and' higher, the benefit of the usel of highly thixotropic mixtures becomes more marked; for example,'a composition high in bentonite or the like, with a high proportion of 'water (such as Mix e) is useful at very high shear points.

This relatively high "percentage application" is particularly important from the cost standpoint, and makes it possible to insulate and protect the inerior of furnaces or the like at a cost commensurate with the beneits gained.

The plastic mix may be applied to the hot surface-in any desired manner, although I have found that the best results are obtained by causing the material to be applied in successive slugs as above described. Numerous forms of apparatus are available for so applying the mixture, but I prefer to employa charging gun of the character illustrated in Fig. 2 for the purpose. Referring to this figure, a generally cylindrical container is indicated at I0. provided with a conical upper end II terminating in a reduced diameter neck I2. An air supply line is brought into the neck I2 at an angle thereto, as at I3, and the neck is then bent over to form a discharge or outlet member I4 to which a supply hose I5 may be attached. The supply hose I5 will'communicate with the delivery pipe, abovementioned, which is introduced into the furnace for application of the plastic mix. The air supply line I3 is preferably provided with a valve I6 and a gauge I'I. A floating piston member I8 is provided in the container I0, preferably together 'with a cup leather or the like I9 so that upon A contained in the cylinder I0 above the piston may of water under pressure is connected to `the underside of the piston I8 .through a supply line l2Il---2|, which is provided with a valve 22 and Compositions lying between'line`L and line'M.

however; show. from' 25 %'-to .50% application (th'e stiiferthe consistency,fgenerally,the greater the"- peroentageapplication) --Gomp'ositions lying loe-J havingemsistenciesw the right'. of

' tween-:line-M and line H showthe Vhighest per``-v centage--applicatiomgfrom 50%; `to,1'75% in actualy-" shear point'is believedto be the Dress.;

preferably with a gauge 23. A valved waste line is provided as at 24 for the release of pressure below the piston I8 when a full charge of material has been dispensed from the cylinder I0. 'I'he cylinder is preferably also provided with a of the furnace interior.` One man is usually emanother man is employed to operate the delivery pipe where the material is actually applied to the furnace surface.

In order to satisfactorily employ plastic mixes of the maximum consistency, I preferably incorporate some excess water with the plastic material when it is charged into the cylinder I0, which excess water will be heterogeneously distributed throughout the plastic material and function as a lubricant as the material is forced.

upward into the outlet member I4 in position tobe acted upon by the air supplied at l 3. These plastic thixotropic mixes of fairly stiff consistency may not readily be diluted with additional water in the absence of a thorough stirring or mixing. I may incorporate this excess water in a body of plastic mix within the cylinder I by the following procedure: The desired quantity of plastic material (about two cubic feet, for example) which is to be charged into the cylinder I 0, is transported to the cylinder from the mixing device in which it was compounded in a wheel barrow (or like container. A quantity of wat-er, such as a half gallon or so, is then poured on top of the plastic mix in the wheel barrow. The cylinder l0 is then charged by dipping with a oneor two-gallon container into the body of plastic mix in the wheel barrow so as to take up some water with each dipper of plastic mix. When these successive dippers-full are charged into the cylinder l0, they will lie in a plurality of separate bodies as at 21, interspaced with layers of water as at 28, which bodies and layers will be of varying sizes and shapes.

The provision of the above-described small proportion of Water in heterogeneous distribution through the pressure chamber of the applicator mechanism has been found to be absolutely essential where the heavier consistency compositions are to be applied. When the consistency exceeds a shear point of about 3000 grams, considerable difficulty is experienced in securing proper ow of material through the delivery pipe by the use of the described apparatus. In this connection, it has been observed that with two mixes of equal shear points, the one having the higher water content will be more susceptible to application, e. g., the mixes shown in Fig. 1 at d and e can be forced through the delivery pipe quite readily, butmixt'ure c and particularly mixture b are very difliculty forced through the apparatus. l

The delivery pipe is conveniently provided with a rather open discharge end, instead of a restricted discharge nozzle as is required with` the relatively thin spray mixes which have hitherto been employed in the art. As a specific example, I have successfully employed a :Mi-inch standard 'black iron pipe for a delivery member, provided with a water jacket extending substantially to the end thereof, and provided with a discharge member consisting of a %inch street L screwed onto the end. This provides a form of directional control, by rotation of the delivery member about its longitudinal axis during the application of the material.

It willbe appreciated that the refractory constituent which makes up the principal proportion of the solids content of the mixtures useful according to this invention may consist of any suitable material having the refractory qualities desired. For example, I have employed highly refractory mixtures by substitution of magnesia 75 plates the use and chromite for the silica, with satisfactory results. The neness of the refractory constituent is of considerable importance with respect to thephysical properties of the final bricked layer produced on the furnace surface. VIt.wil1be appreciated that the use of a finely divided material will result in a finer grained bricked layer, and I have found that for general ,use a ne grained bricked layer is to be preferred, inasmuch as it has a higher heat insulating value in'4 the furnace. The coarse grained bricked layers obtained by the use of coarse refractory aggregate have also been found to exhibit a lower strength in red condition, and a higher proportion of spalling during the conversion to bricked condition. Furthermore, where a coarse refractory constituent is employed, a higher percentage of the highly colloidal clay material is required in order to secure equivalent plasticity, and it will be appreciated that the melting point of the mix is thus correspondingly lowered. Furthermore, comparing fine and 'coarse aggregate mixes of the same consistency from the standpoint of percentage application, the ne aggregate mixes are somewhat to be preferred. The same application technic may be used with the two types of mix; however, I prefer to use air pressure under the piston i8 When a coarse refractory mix is employed to avoid the introduction of excessive amounts of water into the mix within the pressure chamber l0 which has been found `to result from coarse grains of refractory lodging between the piston leather I9 and the side Walls of the chamber, allowing water to pass the piston. Any air which might similarly pass Ler the piston is entirely non-detrimental. Water leakage when usingI ne aggregate mixes is not appreciable. Y

'I'he above-described preference for the use of a nely divided refractory material in the composition is particularly directed to the use of the process in the protection of reverberatory furnaces, where the lining will ordinarily be subjected to a rather strong uxing action as a result of the absorption of mineral particles disseminated in the furnace gases, and it is appreciated that for other types of furnaces, particularly Where no such fluxng condition is present, the coarser grained bricked layers resulting y from the use of relatively coarse refractory aggregate would find marked utility.

It will be further appreciated ,that while I have indicated an upper consistencyV limit in the neighborhood of 3000 grams shear point, this limit is imposed by the mechanics of the char-ging gun or other device employed for the application-of the composition to the furnace surface., Using a charging gun of the typeillustrated in Fig. 2 with air and water pressures in the neighborhood of 100 pounds per square inch, the heavier consistency mixtures which contain in excess of about 35% water can be applied to thefumace surface with a suillcient velocity to secure the desirable plastic deformation of the material upon impingement with the furnace surface. It should be appreciated that operating pressures of 500 pounds per square inchor more would be entirely feasible with the use of a more sturdily constructed charging gun, in which case compositions having shear points materially in excess of 3000 grams could be employed, and that the percentage application" could be expected to exceed or more under such circumstances. M y invention, therefore, contemof plastic argillaceous compositions having shear points above 100 grams, the upper limit on the consistency being restricted only by the mechanical problems attendant the discharge of the material through an adequate nozzle member at a velocity sumcient to secure plastic deformation of the applied material into a plastically adhering contact with the furnace surface.

Other modifications of the invention will occur to those skilled-in the art, and I do not choose to be limited to the specific examples herein described, but rather to the scope of the subjoined claims.

I claim:

1. The method of providing a cellular refractory lining for the interior surfaces of a heated furnace or the like, which comprises: forming an aqueous dispersion of nely divided solid material consisting principally of divided refractory material and containing a highly colloidal argillaceous material, said aqueous dispersion having not less than. about 30% water and a plastic consistency such that the shear point thereof, as

determined by amodifled Stormer viscometer 4heated surface, whereby such plastic thixotropic argillaceous material is caused to 'forcibly im-A Dinge upon such surface in a plurality of successive slugs 2.- The method set forth in claim 1, in'whichy the highly colloidal argillaceous material is of the character of a true bentonite having marked swelling and thixotropic properties.

3. The method set forth in claim 1, in which the highly colloidal argillaceous material is of f/the character of true bentonite having marked n swelling and thixotropic properties and the shear point of said plastic argillaceous dispersion is within the range of about 800 grams to about 2,5,00 grams.

4. The method of providing a cellular refractory lining for the interior surface of a heated furnace or the like which comprises forcibly impinging upon the heated interior surface of such i a furnace a succession of discrete slugs of a plastic aqueous-dispersion of a nely. divided 'A refractory material, containing a highly colloidal argillaceous material and not less than 30% of water, and having a plastic consistency such that the shear point thereof as determined by a "modlifled Stormer viscometer is not less than 5. The method of providing a cellular refractory lining for thev interior surface of a heated furnace or the like which comprises forcibly impinging upon the heated interior surface of such a furnace a succession of discrete "slugs of a plastic aqueous dispersion of a finely divided refractory material, containing a highly colloidal argillaceous material and not less than 30% of water, and having a plastic consistency such that the shear point thereof as determined by a modied Stormer viscometer isl within the `range of about 800 grams to about 2500 grams.

6. The method of providing a cellular refractory lining for the interior surface of a heated furnace or the like which comprises forcibly impinging upon the heated interior surface of such a furnace a succession of discrete "slugs of a i plastic aqueous dispersion of a nely divided refractory material, containing a highly colloidal argillaceous material and not less than 30% of water, and having a. plastic consistency such that the shear point thereof as determined by a modied Stormer viscome is within the range of about 1300 grams to about 2200 grams.

'1. The method of providing a cellular refractory lining for the interior surface of a heated furnace or the like which comprises forcibly impinging upon the heated interior surface of such a furnace a succession of discrete slugs.of a plastic aqueous dispersion of a nely divided refractory material, containing-v from about 3% to about 25% of a highly colloidal arglllaoeous material of the character of "true" bentonite and not less than 30% of water, and having a plastic consistency such that the shear point thereof as determinedl by a modified Stormer viscometer is not less than 100 grams.

8. The method of providing a cellular refractory lining for the interior surface of a heated furnace or the like which comprises forming a plastic aqueous dispersion of nely divided re- -a dispensing chamber-, forcibly discharging al series of successive slugs" of the dispersion from' vsaid chamber and directing the "slugsinto im pingement upon the heated interior surface of such a furnace.

LEONARD LARSON.' 

